Many machines use transmissions to couple the output of a prime mover or power source, for example, an internal combustion engine, to a driven element or device such as wheels or a work implement. Transmissions are typically part of a powertrain that transmits power that may be in the form of torque and/or rotational speed from the power source such as an engine to the driven element. Traditional transmissions typically included one or more fixed, selectably engageable gear ratios that could increase or decrease the speed of the prime mover and, usually in an inverse relationship, the torque. Specific gear ratios often correspond to discrete and known outputs of the transmission, including speed and torque. Accordingly, changing the gear ratio may change the speed and torque characteristics of the machine.
Recently, some manufacturers have equipped machines with continuously variable transmissions (CVTs) instead of the conventional, gear-based transmissions. A CVT provides an infinite or continuous range of torque-to-speed output ratios with respect to any given input from the prime mover. In other words, the output of the CVT can be increased or decreased across a continuous range in almost infinitesimally small increments. Thus, a CVT does not engage specific, discrete gear ratios to determine or control its output. Instead, CVTs provide for new and different ways of changing and adjusting the speed and torque characteristics of the machine. Various control methodologies have been developed to utilize the different capabilities of CVTs for these purposes.
Many machines, whether using a conventional, gear-based transmission or a CVT, are equipped with service brakes to slow or stop the machine. Typical service brakes mechanically engage some portion of the powertrain to resist the rotational power transmission that is driving the propulsion devices and propelling the machine. Service brakes may be used in conjunction with other measures to decrease the output of the machine. For example, U.S. Pat. No. 8,070,651 (the '651 patent) describes a method of braking in a machine equipped with a CVT. If the operator actuates a brake actuator such as a foot pedal, the machine may adjust the input-to-output ratio of the CVT to decrease speed as opposed to physically engaging the service brakes. The '651 patent states that the described method may prolong the service life of the physical brakes. According to the '651 patent service brakes are still typically applied in conjunction with adjusting the CVT input-to-output ratio to decrease speed and stop the machine. However, in some instances, the CVT may respond differently than anticipated when the service brakes are applied. The present disclosure addresses similar considerations regarding the combined use of CVTs and service brakes.